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99

MOLECULAR AND CELLULAR OF ADDICTION

MARY-ANNE ENOCH DAVID GOLDMAN

Worldwide, in societies where moderate alcohol consump- shared among different individuals within the family. Nu- tion is accepted as a pleasurable pastime and even an en- merous studies have shown that alcoholism is familial. In hancer of health and well-being, it has historically been ob- the National Comorbidity Survey of 5,877 individuals, it served that a sizable minority is unable to keep within safe was found that alcohol use disorders aggregate significantly limits of consumption. Such individuals may abuse alcohol in families with an odds ratio of 1.93 (4). To have an alco- or become dependent. Alcoholism is today among the most holic parent is a significant risk factor for the development pervasive psychiatric disorders. In the , the of the disease; children of alcoholics are five times more lifetime prevalence of alcohol dependence, the severe form likely to develop alcohol-related problems than children of of alcoholism, is 8% to 14% (1). The ratio of alcohol depen- nonalcoholics (5). It has been shown that the transmission dence to abuse is 1.5:1. Individuals often maintain a pattern of the vulnerability to alcoholism from parents to their of alcohol abuse without dependence for many years (2). daughters is due largely or entirely to genetic factors (6). Serious drinking frequently begins in adolescence, and ap- Studies of heritability, a measure of the genetic compo- proximately 40% of alcoholics develop their first symptoms nent of variance in interindividual vulnerability, indicate of addiction between the ages of 15 and 19 years (3). As that genetic influences are substantially responsible for the discussed in this chapter, heritability studies suggest that an observed patterns of familiality. Adoption studies have individual’s genotype confers a particular level of vulnerabil- shown that alcoholism in biological parents predicts alco- ity, or risk. Comparative studies across populations suggest holism in children even when the child is reared by unre- that sociocultural factors determine differences in thresholds lated adoptive parents (7,8). Large, well-constructed twin above which an individual is likely to go beyond social studies (8–10) have demonstrated that genetic factors are drinking and slip into abuse or addiction. Is the develop- important in determining vulnerability to alcoholism, par- ment of alcoholism due to a unique set of biochemical and ticularly in the more severe forms of the disease (11). neurobiological determinants or are the causes of addiction Over the past few years, several heritability analyses have common to many substances? Are there preexisting behav- been performed using the population-based Virginia Twin ioral traits that predispose to alcoholism? These are some Registry. A study of 1,030 U.S. Caucasian female twin pairs of the questions addressed by this chapter. demonstrated that whether using narrow, intermediate, or broad definitions, the concordance for alcoholism was con- sistently higher in monozygotic (MZ) than dizygotic (DZ) GENETIC INFLUENCES ON ALCOHOLISM: twin pairs, and the heritability of alcoholism in women is HERITABILITY STUDIES 0.50 to 0.60 (6,9). In a study of 3,516 U.S. male twins, it was found that 0.48to 0.58of the variation in liability Alcoholism is a heterogeneous disease in which the expres- for both alcohol abuse and dependence was attributable to sion of genetic vulnerability is modified by environmental additive genetic factors with the remainder attributable to factors. Some of the environmental influences are uniquely nonshared environmental factors, which is most accurately experienced by the individual (nonshared) and some are labeled as ‘‘other,’’ including as it does other sources of variance such as measurement error (12). The results of these two studies were confirmed in a recent analysis of 5,091 U.S. male twins and 4,168female twins from the Mary-Anne Enoch and David Goldman: Laboratory of Neurogenetics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of same registry (13). This study also added the information Health, Bethesda, Maryland. that the genetic sources of variability are partially, but not 1414 Neuropsychopharmacology: The Fifth Generation of Progress completely, overlapping in men and women. Compared recent evaluation of the co-inheritance of alcoholism and with the expected genetic correlations of 0.5 for same-sex other disorders revealed that the inheritance of alcoholism DZ twin pairs, heritability was 0.20 to 0.24 [95% confi- is remarkably distinct. Female twins from the Virginia Twin ,to 45%] for opposite-sex pairs. Registry were evaluated for alcoholism, MD, BN, phobia 4% ס (dence interval (CI Although the heritability value of approximately 0.5 for al- generalized anxiety disorder (GAD), and panic. Alcoholism cohol dependence in men and women was replicated in emerged as the one disorder with a large disease-specific an analysis of 2,685 male and female twin pairs from the genetic component: approximately 75% of the genetic vari- Australian twin registry (10), no evidence was found for sex ance. In addition, smaller components of the genetic liabil- differences in sources of genetic influence. It may be that ity to alcoholism also loaded onto a factor common to MD the relatively small number of opposite sex pairs—592—in and GAD as well as a factor common to phobia, panic, and the Heath et al. (10) study compared with the larger num- BN (19). ber—1,428—in the Prescott et al. (13) study limited the power to find a difference. COMORBIDITY OF ALCOHOLISM WITH OTHER SUBSTANCE ABUSE: GENETIC GENETIC HETEROGENEITY IN ALCOHOLISM DIATHESES?

Although there is good evidence for substantial heritability Alcohol, cocaine, opiate, and (nicotine) depen- for alcoholism, individual differences in clinical presenta- dency co-occur more often in the population than would tion suggest variation in origins of vulnerability. Alcoholics be expected from their frequencies (20). This raises the pos- vary in their drinking patterns, the severity of their symp- sibility that there may be substance-general, as well as sub- toms, and in behavioral, physical, and psychiatric sequelae. stance-specific, components to the heritability of alcoholism Vulnerability may reside in personality or psychiatric traits (21). that predispose to alcohol-seeking behavior, differential re- Both alcoholism and drug disorders are familial; two sponse to the effects of alcohol, or differential predisposition large studies have evaluated the familial aggregation of alco- to addiction. Vulnerability factors found in some, but by hol and drug dependence (22,23). Both studies found that no means all, alcoholics include attentional deficits reflected relatives of drug-disorder probands across a wide range of by low amplitude of the P300 event-related potential (14), substances, including opioids, cocaine, and cannabis, had a anxiety reflected by the low-voltage alpha EEG trait (15), greater rate of drug disorders themselves than relatives of and diminished subjective response to alcohol (16). controls. However, this comorbidity occurred largely inde- pendently from cotransmission of alcoholism, suggesting that the transmission of alcoholism and other drug disorders COMORBIDITY OF ALCOHOLISM AND is largely independent. OTHER PSYCHIATRIC DISORDERS: GENETIC The strongest evidence of a shared, as well as a specific, DIATHESES? addictive tendency is between alcohol and nicotine. It has long been observed that there is a relationship between Alcohol dependence is often comorbid with other psychiat- smoking and alcoholism. More than 80% of alcoholics ric disorders, including drug abuse, major depression (MD), smoke cigarettes and 70% are heavy smokers, compared anxiety disorders (ADs), and bulimia nervosa (BN), or anti- with 30% of the general population who smoke and 10% social personality disorder (ASPD) (17,18). Lifetime co-oc- who smoke heavily (24). In a multivariate genetic analysis currence is more common among women than men and is of the use of tobacco and alcohol in 774 MZ and 809 DZ positively associated with the persistence of alcohol depen- male and female twin pairs from the Virginia Twin Registry, dence in both men and women (18). Population comorbid- the univariate heritability of alcohol consumption was 0.60 ity, in which two disorders may be observed to co-occur in in men and 0.47 in women, and the heritability of tobacco excess, may be due to shared causation. A strength of genetic use was 0.49 in men and 0.51 in women. Tobacco use had epidemiologic studies is their ability to detect evidence of a stronger loading on this shared genetic factor (0.56 in shared genetic and familial environmental causation. males, 0.49 in females), than alcohol consumption (0.12 in Severe alcoholism, suicidality, and impulsivity tend to males, 0.19 in females) (25). However, the precise level of coexist in the same individuals, usually male. The relative the co-inheritance is less certain than the existence of co- risk of alcoholism is significantly increased in males with inheritance, and the level of genetic sharing may depend either ASPD, attention-deficit/hyperactivity disorder, or on how the phenotypes are determined. In an analysis of childhood conduct disorder, and there is evidence of co- 2,220 MZ and 2,373 DZ U.S. male twin pairs from the inheritance of ASPD and alcoholism. Alcoholism in women National Academy of Sciences–National Research Coun- is associated with anxiety and affective disorders (18) and cil’s World War II Twin Registry, a heavy smoking, heavy increased neuroticism (10). These data notwithstanding, a alcohol genetic factor accounted for 0.45 of the heritable Chapter 99: Molecular and Cellular Genetics of Alcohol Addiction 1415 variance in heavy drinking and 0.35 of the heritable variance to release of in the NA (32), but the rewarding in heavy smoking (26), and substance-specific genetic influ- effects are also mediated by the cholinergic and serotoniner- ences contributed 0.22 of the total heritable variance in gic systems. The acute reward effects of heavy smoking and 0.55 for heavy alcohol use (26). A study opioids are enhanced by activation of ␮ (and possibly also of 3,356 male twin pairs from the U.S. Vietnam Era Twin ␦) receptors in the VTA. -Enhanced ␥-aminobutyric acid (GABA), glutamate, do (0.68 ס Registry found a substantial genetic correlation (r between alcohol and nicotine dependence. Of the total vari- paminergic, opioid , and serotoninergic neurotrans- ance in risk for alcohol dependence, 0.26 was common with mission have been associated with acute ethanol administra- the genetic influence on nicotine dependence (27). tion, and potentially mediate some of alcohol’s reinforcing effects (33). In contrast to opioids, which bind to specific receptors, ethanol appears to act on a variety of targets THE NEUROBIOLOGY OF ALCOHOL within the in a less specific manner, inducing ADDICTION effects on neurotransmitter and membrane receptors and receptor-gated and voltage-activated ion The essential features of addiction are loss of control over channels as well as modulating neurotransmitter release consumption, compulsion to obtain the next stimulus, and (34). Alterations in calcium channels may be a major com- continuation of abuse despite knowledge of negative health ponent of the changes that occur in the physical dependence and social consequences. Tolerance and dependence are due on ethanol (35). to neuroadaptations. Processes of reward and reinforcement GABA is the major inhibitory neurotransmitter in brain. play their most crucial role at the start of the path to addic- The development of tolerance may be related to ethanol- tion, after which long-lasting or permanent neuroadapta- induced adaptive changes in the GABAA receptor system. tions occur. It is likely that genetic variation in this neurobi- GABAA receptors are the primary site of action of benzodi- ology predisposes some individuals to a pattern of increased azepines and , which are used in the treatment craving and loss of control. of alcohol withdrawal symptoms. Addictive substances affect a range of neurotransmitter Increasing evidence suggests that ethanol’s inhibition systems in different regions of the brain. However, a path- of the glutamatergic neurotransmitter pathways, especially way that appears to be crucial to the action of all addictive at the level of the postsynaptic N-methyl-D-aspartate drugs is the mesolimbic dopamine system, which originates (NMDA) receptor, may be an important cause of its neu- in the ventral tegmental area (VTA) of the midbrain and rotoxic effects (36). Glutamate is the major excitatory brain projects to the nucleus accumbens (NAC), with projections neurotransmitter with up to 40% of all synapses being gluta- also to the limbic system and the orbitofrontal cortex (28). matergic (36). Inhibition of GABAergic interneurons me- The amygdala, hippocampus, and medial prefrontal cortex diated via ethanol’s effect on the NMDA receptor may result send excitatory projections to the NAC. The mesolimbic in disinhibition of forebrain glutamatergic that dopamine pathway is associated with the ability to feel plea- augment dopamine release (37). Changes in the NMDA sure. Serotoninergic neurons originating in the dorsal and median project to mesolimbic structures, in- receptor system may underlie intoxication and withdrawal cluding the VTA and NAC, and may exert inhibitory con- symptoms (38) as well as ‘‘blackouts’’ (36). Homotarrine trol on mesolimbic dopamine activity (29) (see (Acamprosate), a structural analogue of glutamate and an Chapter 95). NMDA-receptor antagonist, has been shown to almost dou- Alcohol, psychostimulants, opiates, and nicotine (as well ble the abstinence rate in recovering alcoholics (39). Some of the rewarding effects of ethanol result from acti- as tetrahydrocannabinol and phencyclidine) exert their pri- ␮ ␦ mary reinforcing or reward effects by releasing dopamine vation of opioid receptors in the VTA and/or receptors (DA) in the NAC. The acute reinforcing actions of psycho- in the NAC by the ethanol-induced release of endogenous ␤ stimulant drugs is mediated both by the blockade of DA -endorphin from terminals of the VTA and NAC as well binding to its transporter, preventing the reuptake of DA as release of enkephalins from intrinsic enkephalin neurons from the synaptic cleft (20), and by interaction with multi- in the NAC (34). The success of the opioid antagonist nal- ple DA receptors including D1, D2, and D3 (28). Cocaine trexone in modifying drinking behavior, controlling craving blocks the reuptake of (5-HT) and norepineph- and preventing relapse in alcoholics indicates that opioid rine in a similar fashion. A functional down-regulation of receptor-mediated mechanisms are activated by alcohol (34, 5-HT3 receptors in the NAC may contribute to cocaine 40). tolerance (30), whereas chronic alcohol intake increases the The co-inheritance of nicotine and alcohol dependence sensitivity of 5-HT3 receptors (31). Chronic cocaine and (27) may relate to the finding that ethanol enhancement of alcohol administration also disrupts the endogenous opioid DA release in the NAC appears to require activation of system (20). Nicotine’s reinforcing effect is through activa- nicotinic receptors in the VTA. Neuronal nicotinic acetyl- tion of nicotinic receptors in the VTA, ultimately leading choline receptors are structurally related to GABAAreceptors 1416 Neuropsychopharmacology: The Fifth Generation of Progress

(41). Activation of these nicotinic receptors may enhance the development of alcoholism. One gene variant (allele) is ethanol reinforcement and voluntary intake (42). protective and the other is a vulnerability allele. Alcohol Some studies have implicated involvement of the seroto- dehydrogenase (ADH) metabolizes ethanol to acetaldehyde, nin receptors 5-HT3 and possibly 5-HT4 in DA release a toxic intermediate, which is in turn converted to acetate in the NAC (31,43). 5-HT3 is the only known serotonin by aldehyde dehydrogenase (ALDH). Approximately half receptor that directly gates an ion channel and hence ethanol the population of Southeast (SE) Asian countries such as directly potentiates the effects of serotonin at this site (44). China, Japan, and Korea have functional polymorphisms at Chronic alcohol intake increases the sensitivity of 5-HT3 four different genes: ADH2, ADH3, ALDH1, and ALDH2. receptors (31) and results in enhanced GABAergic activity. Across populations, the ALDH2-2 variant appears on a sim- The 5-HT3 antagonist has been shown to re- ilar genetic background (haplotype) and thus has probably duce alcohol consumption in alcoholics (45). had the same evolutionary origin (47). The most important variants are ALDH2-2 (Glu487–Lys487) and ADH2-2 GENETIC STUDIES OF ALCOHOLISM IN (Arg47–His47). ALDH2-2 dominantly inactivates ALDH2, HUMANS the ALDH that is mitochondrially localized and responsible for most acetaldehyde in cells. ADH2-2 is a In a heterogeneous disease such as alcoholism it is likely superactive variant. Allelic variation at ADH3 apparently that there are different environment-related thresholds and exerts no independent effect on the risk for alcoholism; different genes and gene variants. In addition there could however, ADH3-1 is in linkage disequilibrium with ADH2- be additive or nonadditive (epistatic) interactions between 2 (48,49) and is thus also predictive of vulnerability. ADH2- variants of multiple genes. Classic genetic analyses in ro- 2 and ALDH2-2 raise the levels of acetaldehyde by increas- dents show that certain alcohol-related phenotypes (e.g., ing the rate of synthesis, by decreasing the rate of metabo- alcohol sensitivity) can be polygenic. On the other hand, lism, and by interacting additively, but not synergistically human data showing an approximately 2:1 MZ/DZ twin (50). The result is that ingestion of even small amounts of ratio of concordance for alcoholism and high recurrence ethanol produces an unpleasant reaction characterized by rates in first-degree relatives of alcoholics followed by a pro- facial flushing, , hypotension, palpitations, tachy- gressively decreasing risk in proportion to relatedness are cardia, , and vomiting (51). In an analogous fashion, compatible with additivity of inheritance, and do not favor , used in the treatment of alcoholism, and some multiple genes. The alcoholism genes identified so antiprotozoal drugs such as metronidazole, inhibit ALDH2 far—ALDH2 and ADH2—were discovered individually and thereby cause a flushing reaction after alcohol consump- but act additively when they co-occur (vide infra). tion. Therefore, the protective effect of ALDH2 genotypes To dissect the multiple genetic influences on alcoholism can be regarded as analogous to protection with disulfiram, vulnerability, it may be necessary or useful to consider sev- as this flushing reaction, severe in homozygotes but milder eral phenotypes representing different aspects of the disease. in heterozygotes, deters individuals with the protective al- Attempts have been made to classify alcoholics into more leles from becoming alcoholic. The allele frequency of the homogeneous clinical groups by severity (dependence or dominantly acting ALDH2-2 is 0.3 in Japanese and abuse), withdrawal signs, tolerance, medical sequelae, or la- Chinese, and hence about one in two individuals experience tent class phenotypes. Cloninger (46) divided alcoholics on flushing after alcohol consumption. Their risk of alcoholism a clinical and genetic epidemiologic basis into type 1 (mi- is reduced about four- to tenfold. Approximately 10% of lieu-limited, later onset) and type 2 (early onset, male domi- Japanese are ALDH2-2/ALDH2-2 homozygotes. Thus far, nated, associated with ASPD), thus linking premorbid per- only one alcoholic ALDH2-2/ALDH2-2 homozygote has sonality with alcoholism vulnerability and identifying an been observed across a series of studies in which several alcoholism subtype, type II, with a stronger genetic predis- hundred alcoholics have been genotyped, and that individ- position. This classification is supported by a study involv- ual is the focus of a report (52). ing the National Comorbidity Survey of 5,877 people in The genetic influence of ALDH2 variants on alcohol which Kendler et al. (4) demonstrated that there are two consumption is modified by environment. Tu and Israel underlying dimensions of liability for alcoholism, drug dis- (53) found that acculturation accounted for some of the orders, ASPD, MD, and GAD that are familially transmit- variance (7–11%) in alcohol consumption for SE Asian ted with moderate specificity: (a) chronic dysphoric symp- males born in North America, although the ALDH2 poly- toms of anxiety and depression, and (b) acting-out behaviors morphism predicted two-thirds of the alcohol consumption and harmful substance use. and excessive alcohol use. Also, there are large differences in the prevalence of alcohol dependence in populations that GeneticsOf Alcohol Metabolism have similar ALDH2 allele frequencies. The frequencies of At the present time, the genes for alcohol metabolism are the ADH2 and ALDH2 variants are similar, but the preva- the only genes that are known to have a major impact on lence of alcoholism is 2.9% in Taiwan and and 17.2% in Chapter 99: Molecular and Cellular Genetics of Alcohol Addiction 1417

TABLE 99.1. THE RELATIONSHIP OF ALDH2 disorders (15). Such endophenotypes may be influenced by AND ADH2 GENOTYPES AND THE RISK FOR variation at fewer genes. The brain is relatively inaccessible, ALCOHOLISM IN SOUTHEAST ASIANS (48) so it has been more difficult to obtain biochemical and ALDH2 ADH2 Protective Factor physiologic measures that identify more specific genetic sub-

∗ ∗ ∗ ∗ ∗ ∗ ∗ ∗ types as was done decades ago for certain other common, 2/ 2 2/ 2, 1/ 2, or 1/ 1 High broadly defined diseases (e.g., anemia). Association studies ∗2/∗1 ∗2/∗2 or ∗2/∗1 ∗1/∗1 of candidate genes, although laborious, have far greater ∗1/∗1 ∗2/∗2 power for untangling the genetics of complex diseases than ∗2/∗1 linkage analysis (60). New approaches, including TDT ∗1/∗1 None (transmission disequilibrium test) analysis (61,62) and eth- nic matching using informative markers (63), have been ADH, alcohol dehydrogenase; ALDH, aldehyde dehydrogenase. used to avoid the problems of population stratification, i.e., ethnic mismatching of cases and controls.

Korea, suggesting that there are interactions with other ge- Rodent Models: Quantitative Trait Locus netic and environmental factors (54). Analyses The ADH2 genotype has been shown to be an indepen- Rodent strains are inbred to produce large numbers of ge- dent factor contributing to the risk of alcoholism (50) and netically identical animals that can be maintained under acts additively with the ALDH2-2 variant (Table 99.1). A controlled environmental conditions and intercrossed when pilot study found that the ADH2-2 allele accounts for 20% required. The neurobiology of reinforcement and reward to 30% of the alcohol intake variance between two groups of was elucidated largely through behavioral and anatomic light-drinking and heavy-drinking Israeli Jews, and suggests studies in rodents. Several behavioral traits in rodents are that the relatively high frequency of the ADH2-2 allele continuous and polygenic. Each of the multiple genes re- might contribute to the generally perceived lower levels of sponsible for such quantitative traits is termed a quantitative alcohol consumption and increased sensitivity to alcohol trait locus (QTL). Several QTLs may influence one trait, observed among Jews (55,56). one QTL may affect several traits, and these QTLs can be The ADH2-3 allele is a high activity variant identified individually mapped, with the ultimate goal being to iden- in approximately 25% of African-Americans, which in- tify genes that play a role in human addiction to alcohol. creases the rate of ethanol metabolism (57). In one report, The knockout of an individual gene in the mouse can reveal the presence of ADH2-3 in African-American mothers a potential role for the equivalent (homologous) gene in the drinking during pregnancy was associated with a lower rate human. of alcohol-related birth defects (58). Several QTLs for alcohol-associated behaviors have been identified in mice by using recombinant inbred strains that differ widely with respect to many alcohol-related traits, and DETERMINING THE GENETIC BASIS OF by follow-up studies using interstrain crosses and congenics. VULNERABILITY TO ALCOHOLISM The behaviors for which QTLs have been mapped include acute and chronic alcohol withdrawal sensitivity, alcohol Genetic analysis of complex disorders is complicated by the consumption, and alcohol-associated hypothermia. Buck et fact that any single gene is likely to account for only a small al. (64) have shown that 68% of the genetic variability for part of the variance. To detect subtle genetic effects, large genes influencing alcohol withdrawal severity can be as- samples are needed. The four methods (59) most widely signed to QTLs on mouse chromosomes 1, 4, and 11. The used are (a) linkage analysis: the inheritance pattern of phe- locus on chromosome 11 accounted for 12% of the genetic notypes and genotypes are elucidated in pedigrees; (b) allele variability in withdrawal liability and was near the genes for ␥ ␣ ␣ sharing methods: affected relatives are compared to detect the 2, 1, and 6 subunits of GABAA receptors. Further- ␥ excess genotype sharing; (c) association (case-control) stud- more, a 2 subunit polymorphism has now been found to ies: unrelated affected and unaffected individuals are com- be genetically correlated with alcohol withdrawal severity in pared; (d) analysis of inbred, transgenic, and gene-knockout mice (65). QTLs for alcohol-induced hypothermia, alcohol animals (principally mice and rats). consumption, and certain responses to and Linkage analysis has been successfully employed in find- morphine are located on chromosome 1 (66) and also on ing major genes in diseases such as Huntington’s disease, chromosome 9 near the serotonin 5-HT1B receptor and do- but it has limited power to detect genes of modest effect pamine D2 receptor genes (67). These genetic interrelation- (60). An alternative approach is to employ an endopheno- ships between different phenotypes indicate that the same type as a trait specific marker, e.g., the low-voltage alpha genes influence different alcohol-associated behaviors, that EEG trait that is associated with alcoholism and anxiety several genes may affect one phenotype, and that some loci 1418 Neuropsychopharmacology: The Fifth Generation of Progress for drug abuse are not drug specific. This is also evident in holism, any genetic determinants of vulnerability to alcohol- studies of mice in which specific genes that map to the QTL ism and sensitivity to alcohol’s effects are likely to be subtle. regions or candidate genes located elsewhere in the mouse genome have been knocked out. 5-HT knockout mice 1B Serotonin drink twice as much ethanol, are less intoxicated, and show enhanced aggression compared with normal mice (68). On Serotonin is involved in behavioral inhibition and is a target chronic exposure to alcohol they show less evidence of toler- for the pharmacologic treatment of alcoholism. Selective ance. These mice also work harder to self-administer cocaine serotonin reuptake inhibitors play a limited role in modify- and show an increased locomotor response, behaving as if ing craving for alcohol and also modify other comorbid already sensitized to the drug (69). behaviors such as depression and anxiety. The dopamine-related genes that have been knocked out Pathologically low levels of serotonin may contribute to in mice are the DRD4 dopamine receptor, which is located impulsivity and ASPD; for example, a group of criminal, at the site of one of the alcohol QTLs, the D1 and D2 alcoholic Finns was shown to have low dopamine receptors, the dopamine transporter, and (CSF) 5-hydroxyindolacetic acid (5-HIAA), the lowest lev- VMAT2 (the vesicular transporter). The DRD4 knockout els being found in those who had committed impulsive mice appear to be supersensitive to ethanol, cocaine, and crimes (75). These are the alcoholics who would be most amphetamine (70). Mice lacking the D2 receptor consume likely to have a serotonin gene variant affecting function. less alcohol than normal mice (71). VMAT2 knockout mice have a pronounced supersensitivity to cocaine, amphet- Serotonin Transporter , and ethanol (72). The availability of brainstem serotonin transporter, mea- For morphine preference, three loci identified on murine sured by (I-123) ␤-CIT and single photon emission com- chromosomes 1, 6, and 10 are apparently responsible for puted tomography, has been found to be significantly re- nearly 85% of the genetic variance in this trait (73). The duced in alcoholics, and correlated with ratings of ␮ opioid receptor gene is located at the site of the largest depression and anxiety during withdrawal (76). A functional QTL, and this QTL also affects consumption of alcohol polymorphism, 5-HTTLPR, in the serotonin transporter and cocaine (73). promoter region (77) has been associated fairly consistently QTL analysis in rodents has limitations. Frequently the with anxiety/dysphoria (77,78). Several association analyses result is a large genomic region of interest rather than a have shown that the s-allele, which reduces transcriptional gene. There may be functional compensation in knockout efficiency, is increased in French alcoholics (79), severely mice during development. Mice and humans may not share affected German alcoholics (80), and early-onset, violent the same functional variants at the same allele; for example, Finnish alcoholics with ASPD (81). However, neither link- the ALDH2-2 allele is not even present in all human popu- age nor association for the s-allele was found in a family- lations and is not found in mice. Another problem is that based TDT analysis of U.S. alcoholics from the COGA behaviors in mice cannot be freely extrapolated to humans; (Collaborative Study on the Genetics of Alcoholism) data for example alcohol preference in mice may well be taste set, some with withdrawal symptoms (82). A Japanese asso- preference (74). However, QTL analyses in mice are useful ciation study of alcoholics with withdrawal seizures was also for the identification of candidate genes and gene regions. negative (83), and in a small study the long allele was found to be associated with reduced sensitivity to alcohol, i.e., with individuals who may be more vulnerable to developing alcoholism (84). Population stratification may be a problem GENETICS OF REWARD NEUROCIRCUITS, with these association studies as allele frequencies have been AND NEUROCIRCUITS REGULATING shown to vary in European-American, African-American, IMPULSE CONTROL and Japanese populations (85). Candidate Gene Approach: Case-Control Association Studies Serotonin-Metabolizing Enzymes A hydroxylase (TPH) intron variant that affects A logical approach to understanding vulnerability to alcohol splicing is associated with reduced 5-HIAA and suicidality addiction is to look directly for variants in genes involved in impulsive alcoholics (86,87). in neurotransmitter pathways implicated in ethanol use. Of particular interest is the reward pathway, incorporating sero- Serotonin Receptors toninergic, GABAergic, dopaminergic, opioid, and gluta- Several serotonin receptors are known to be abundant in matergic neurotransmission, and the largely serotoninergic the NAC: 5-HT1B, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6. impulse-control pathway. Genes for neurotransmitter me- There are as yet few published studies in which these seroto- tabolizing enzymes, transporters, and receptors are good nin receptors have been genotyped in humans. candidates. Because of the complexity of causation of alco- Studies in rats suggest that activation of 5-HT1B recep- Chapter 99: Molecular and Cellular Genetics of Alcohol Addiction 1419

tors in the NAC may be inhibitory on the behavioral effects transcriptionally significant promoter polymorphisms offer of elevated mesolimbic dopamine transmission (88) by promising tools for understanding the roles of DRD2 (101) primarily modulating the activity of glutamatergic hip- and DAT (102) in alcoholism. pocampo-accumbens pathways and only secondarily alter- ing NAC DA levels (89). In a large sib-pair linkage analysis Opioid Receptors of Finnish alcoholic criminal offenders, significant evidence ␮ ␦ ␬ of linkage and association of antisocial alcoholism to Three endogenous opioid receptors ( , , and ) are the ␤ HTR1B G861C was found, and this was also observed in targets of the major opioid ( -endorphin, enke- a Southwest American Indian tribe, suggesting that a locus phalins, and dynorphins, respectively). The rewarding prop- ␮ ␦ predisposing to antisocial alcoholism may be linked to erties of - and -receptor ligands are brought about by HTR1B at 6q13-15 (90). activation of the mesolimbic dopamine system. Activation ␬ Activation of 5-HT receptors inhibits DA release in of receptors is dysphoric. Human and animal studies im- ␮ the NAC (91). However, the functional Cys23Ser polymor- plicate the opioid system, particularly the opioid receptor, phism does not appear to be associated with alcohol depen- in both initial sensitivity or response to alcohol, and in the dence (92). rewarding or reinforcing effects of alcohol. Subjects at high 5-HT receptors may be involved in several facets of risk for alcoholism have been shown to have lower basal 3 ␤ alcohol-seeking behavior, alcohol intoxication, and addic- plasma -endorphin levels but a more pronounced release tion (93); however, at the present time there are no pub- after exposure to ethanol (103). Some studies have found associations of the gene encoding the ␮ opioid receptor, lished studies on the role of 5-HT3 variants in alcoholics. OPRM1, with some form of drug dependence (104). How- ever, association and sib-pair linkage analyses of Asn40Asp, GABA Receptors a ␮ opioid receptor polymorphism, in 100 U.S. Caucasians, Cross-tolerance of with ethanol and their 324 Finnish Caucasians, and 367 American Indians showed effectiveness in treating alcohol withdrawal suggests that no significant association, even though the study had 80% power to detect a small to moderate effect of OPRM1 varia- GABAA receptors play a key role in alcohol’s effects. The tion on alcohol dependence (105). Findings were also nega- GABAA receptor exists as a number of subtypes that are composed of combinations of at least 14 different subunits. tive from a large study of German alcoholics (106) and Preliminary studies indicate that the Pro385Ser substitution a study of 891 drug- or alcohol-dependent subjects from ␣ African-American, European-American, and Hispanic in GABAA 6 may play a role in sensitivity (94) and may be associated with a lower level of response origins (107). to the acute effects of alcohol (84). Several studies have ␣ found associations between GABAA 6 and alcohol depen- NMDA Receptors dence (84,95) and antisocial alcoholism (96). Differences At the present time there are no published studies on the in allele frequencies between alcoholics and controls have role of NMDA variants in alcoholism. Such studies would been found in GABA ␣3 but not in a GABA ␣1 (97). A A be of interest because of the role of NMDA receptors in There are positive (95) and negative (96) association studies reward, intoxication, and withdrawal, and potentially for for GABA ␤2 and alcohol dependence. A the pharmacogenetics of acamprosate.

Dopamine Nicotinic Receptors Dopamine is involved in arousal, reward, and motivation. Two classes of neuronal nicotinic acetylcholine receptor Structural variants, some altering function or level of expres- (nAchR) subunits (eight ␣ and three ␤) have been identified sion of gene product, have been found in the dopamine (108). The most abundant receptor subtype in brain is com- transporter (DAT) and in several dopamine receptor genes ␤ ␣ posed of 2 and 4 subunits (109). Several lines of evidence, (DRD2, DRD3, and DRD4). At the present time, no role including drug preference in knockout mice (110), suggest for variation in dopamine-related genes in alcoholism has ␤ that the nAchR 2 subunit gene (CHRNB2) is involved in been consistently demonstrated. The controversial associa- the reinforcing properties of nicotine. However, none of tion of a DRD2 dopamine receptor polymorphism with the CHRNB2 variants found so far in humans has been alcoholism has been replicated in some case-control studies associated with nicotine dependence (109). This gene has but not in numerous others (98), nor was it supported in yet to be genotyped in alcoholics. two very large family linkage studies (99), one of which used the functionally impaired 311Cys variant. These fam- Whole Genome Linkage Scans ily studies were not subject to the potential problems of ethnic stratification inherent in some of the DRD2 case- The power of the genetic linkage analysis approach has been control association studies (100). Two recently discovered greatly improved by the recent collection of very large, care- 1420 Neuropsychopharmacology: The Fifth Generation of Progress fully phenotyped, family and population data sets such as transmission have been associated with acute ethanol ad- that of COGA, a multicenter, family genetic study and the ministration and potentially mediate some of alcohol’s rein- National Institute on Alcohol Abuse and Alcoholism forcing effects. Genetic variants in the serotoninergic (NIAAA) Southwestern Indian family sample. Two studies system—5-HT1B , TPH, and possibly 5-HTTLPR—have utilizing these data sets have detected evidence of linkage been associated with alcoholism, particularly in males with of alcoholism to several chromosomal regions, with some antisocial, impulsive features. Several studies have found ␣ convergent findings (111,112). In the Southwestern Ameri- associations between GABAA 6 and alcohol dependence. can Indian population isolate, suggestive evidence was There have been no conclusive genetic findings in the dopa- found for linkage of alcohol dependence to the ADH region minergic or opioid systems to date. on chromosome 4q and to two regions harboring neuroge- Future studies are likely to focus on finding genetic var- netic candidate genes. Those locations were chromosome iants in the neuroreceptors and ion channels that have been 11p, in close proximity to the DRD4 dopamine receptor demonstrated to be affected by ethanol, including GABAA and hydroxylase gene (the rate-limiting enzyme in receptors, NMDA receptors, non-NMDA glutamate recep- dopamine ), and chromosome 4p, near a GABA tors, 5-HT3 receptors, voltage-gated calcium channels, and receptor gene cluster (111). In the COGA families, which neuronal nACh receptors. Of particular interest will be derive from the cosmopolitan, diverse population of the functional genetic variants that are directly capable of alter- United States, modest evidence was also found of linkage ing reward, tolerance, and withdrawal, thereby predisposing to the ADH region on 4q. There was also evidence of link- individuals to addiction to alcohol. age to chromosomes 1 and 7, and to chromosome 2 at the location of the opioid receptor gene (112). In addition, there was evidence of linkage of the P300 event-related po- tential alcoholism-associated trait to chromosome 6q in the REFERENCES region of a glutamate receptor (GRIK2), and to chromo- 1. American Psychiatric Association. Diagnostic and statistical man- some 2q near the location of two acetylcholine receptors ual of mental disorders, fourth ed. Washington DC: American (113). Psychiatric Press, 1994. 2. Schuckit MA, Smith TL, Danko GP, et al. Five-year clinical course associated with DSM-IV alcohol abuse or dependence in a large group of men and women. Am J Psychiatry 2001; DISCUSSION 158(7):1084–1090. 3. Helzer JE, Burnam A, McEvoy LT. Alcohol abuse and depen- There is abundant evidence of substantial heritability (0.5 dence. In: Robins L, Reiger D, eds. Psychiatric disorders in to 0.6) of both broad and narrow definitions of alcoholism America: the Epidemiological Catchment Area Study. New York: Macmillan, 1991:81–115. in men and women. Although the quantitative role of ge- 4. Kendler KS, Davis CG, Kessler RC. The familial aggregation netic risk factors is approximately equal in both sexes, the of common psychiatric and substance abuse disorders in the lower concordance of opposite-sex pairs suggests some gen- National Comorbidity Survey: a family history study. Br J Psy- der-specific action of genes. chiatry 1997;170:541–548. Genetic vulnerability to alcoholism may originate in per- 5. Midanik L. Familial alcoholism and problem drinking in a na- tional drinking survey. Addict Behav 1983;8:133–141. sonality or psychiatric traits that predispose to alcohol-seek- 6. Kendler KS, Neale MC, Heath AC, et al. A twin-family study of ing behavior, differential response to the effects of alcohol, alcoholism in women. Am J Psychiatry 1994;151(5):707–715. or differential predisposition to addiction. Studies of the 7. Goodwin DW. Alcoholism and heredity. Arch Gen Psychiatry co-inheritance of alcoholism and other psychiatric disorders 1979;36:57–61. are beginning to emerge. There is evidence of co-inheritance 8. Heath AC. Genetic influences on alcoholism risk. A review on adoption and twin studies. Alcohol Health Res World 1995;19(3): of ASPD and alcoholism in men. Although alcoholism is 166–171. associated with anxiety and affective disorders in women, 9. Kendler KS, Heath AC, Neale MC, et al. A population-based it has been shown that 75% of the genetic variance of alco- twin study of alcoholism in women. JAMA 1992;268(14): holism is disease specific. Alcohol, nicotine, and other sub- 1877–1882. stance abuse disorders have been noted to co-occur, yet re- 10. Heath AC, Bucholz KK, Madden PAF, et al. Genetic and envi- cent studies have shown that the transmission of alcoholism ronmental contributions to alcohol dependence risk in a na- tional twin sample: consistency of findings in women and men. is largely independent of that of other drugs of abuse with Psychol Med 1997;27:1381–1396. the exception of nicotine, with which there is a substantial 11. Cloninger CR, Bohman M, Sigvardsson S. Inheritance of alco- (0.68) genetic correlation. hol abuse: cross-fostering analysis of adopted men. Arch Gen The mesolimbic dopamine system is fundamental to the Psychiatry 1981;38:861–868. neurobiology of addiction. We are only at the very begin- 12. Prescott CA, Kendler KS. Genetic and environmental contribu- tions to alcohol abuse and dependence in a population-based ning stages of understanding the complexities of ethanol’s sample of male twins. Am J Psychiatry 1999;156(1):34–40. interactions with this system. Enhanced GABA, glutamate, 13. Prescott CA, Aggen SH, Kendler KS. Sex differences in the dopaminergic, opioid peptide, and serotoninergic neuro- source of genetic liability to alcohol abuse and dependence in Chapter 99: Molecular and Cellular Genetics of Alcohol Addiction 1421

a population-based sample of U.S. twins. Alcohol Clin Exp Res 34. Herz A. Endogenous opioid systems and alcohol addiction. Psy- 1999;23(7):1136–1144. chopharmacology 1997;129:99–111. 14. Begleiter H, Porjesz B, Bihari B, et al. Event-related brain po- 35. Little HJ. The role of calcium channels in drug dependence. tentials in boys at risk for alcoholism. Science 1984;225: Drug Alcohol Depend 1995;38:173–194. 1493–1495. 36. Tsai G, Coyle JT. The role of glutamatergic neurotransmission 15. Enoch M-A, White KV, Harris CR, et al. Association of low- in the pathophysiology of alcoholism. Annu Rev Med 1998;49: voltage alpha EEG with a subtype of alcohol use disorders. 173–184. Alcohol Clin Exp Res 1999;23(8):1312–1319. 37. Nestler EJ, Hope BT, Widnell KL. Drug addiction: a model 16. Schuckit MA. Low level of response to alcohol as a predictor for the molecular basis of neural plasticity. Neuron 1993;11: of future alcoholism. Am J Psychiatry 1994;151(2):184–189. 995–1005. 17. Regier DA, Farmer ME, Rae DS, et al. Comorbidity of mental 38. Koob GF, Roberts AJ, Schulteis G, et al. Neurocircuitry targets disorders with alcohol and other drug abuse: results from the in ethanol reward and dependence. Alcohol Clin Exp Res 1998; Epidemiologic Catchment Area (ECA) Study. JAMA 1990;264: 22(1):3–9. 2511–2518. 39. Sass H, Soyka M, Mann K, et al. Relapse prevention by acam- 18. Kessler RC, Crum RM, Warner LA, et al. Lifetime co-occur- prosate. Results from a -controlled study on alcohol de- rence of DSM-III-R alcohol abuse and dependence with other pendence. Arch Gen Psychiatry 1996;53:673–680. psychiatric disorders in the National Comorbidity Survey. Arch 40. O’Malley SS. Opioid antagonists in the treatment of alcohol Gen Psychiatry 1997;54:313–321. dependence: clinical efficacy and prevention of relapse. Alcohol 19. Kendler KS, Walters EE, Neale MC, et al. The structure of the Alcohol 1996;31(Suppl. 1):77–81. genetic and environmental risk factors for six major psychiatric 41. Narahashi T, Aistrup GL, Marszalec W, et al. Neuronal nico- disorders in women. Arch Gen Psychiatry 1995;52:374–383. tinic acetylcholine receptors: a new target site of ethanol. Neuro- 20. Kreek MJ. Cocaine, dopamine and the endogenous opioid sys- chem Int 1999;35(2):131–141. tem. J Addict Dis 1996;15(4):73–96. 42. Harris RA. Ethanol actions on multiple ion channels: which 21. Goldman D, Bergen A. General and specific inheritance of sub- are important? Alcohol Clin Exp Res 1999;23(10):1563–1570. stance abuse and alcoholism. Arch Gen Psychiatry 1998;55(11): 43. Mylecharane EJ. Ventral tegmental area 5-HT receptors: meso- 964–965. limbic dopamine release and behavioral studies. Behav Brain 22. Bierut LJ, Dinwiddie SH, Begleiter H, et al. Familial transmis- Res 1996;73(1–2):1–5. sion of substance dependence: alcohol, marijuana, cocaine and 44. Grant KA. The role of 5-HT3 receptors in drug dependence. habitual smoking. Arch Gen Psychiatry 1998;55:982–988. Drug Alcohol Depend 1995;38:155–171. 23. Merikangas KR, Stolar M, Stevens DE, et al. Familial transmis- 45. Sellers EM, Tonetto T, Romach MK, et al. Clinical efficacy of sion of substance use disorders. Arch Gen Psychiatry 1998;55: the 5-HT3 antagonist ondansetron in alcohol abuse and depen- 973–979. dence. Alcohol Clin Exp Res 1994;18:879–885. 24. NIAAA. Alcohol and tobacco. In: Alcohol alert. Washington, 46. Cloninger CR. Neurogenetic adaptive mechanisms in alcohol- DC: NIAAA, 1998;39:1–4. ism. Science 1987;236:410–416. 25. Hettema JM, Corey LA, Kendler KS. A multivariate genetic 47. Peterson RJ, Goldman D, Long JC. sequence diver- analysis of the use of tobacco, alcohol and caffeine in a popula- sity in non-coding regions of ALDH2 as revealed by restriction tion-based sample of male and female twins. Drug Alcohol De- enzyme and SSCP analysis. Hum Genet 1999;104(2):177–87. pend 1999;57(1):69–78. 48. Chen CC, Lu RB, Chen YC, et al. Interaction between the 26. Swan GE, Carmelli D, Cardon LR. Heavy consumption of functional polymorphisms of the alcohol-metabolism genes in cigarettes, alcohol and coffee in male twins. J Stud Alcohol 1997; protection against alcoholism. Am J Hum Genet 1999;65(3): 58:182–190. 795–807. 27. True WR, Xian H, Scherrer JF, et al. Common genetic vulnera- 49. Osier M, Pakstis AJ, Kidd JR el al. Linkage disequilibrium at bility for nicotine and alcohol dependence in men. Arch Gen the ADH2 and ADH3 loci and risk of alcoholism. Am J Hum Psychiatry 1999;56:655–661. Genet 1999;64(4):1147–1157. 28. Koob GF, Le Moal M. Drug abuse: hedonic homeostatic dysreg- 50. Thomasson HR, Edenburg HJ, Crabb DW, et al. Alcohol and ulation. Science 1997;278:52–58. aldehyde dehydrogenase genotypes and alcoholism in Chinese 29. Di Matteo V, Di Giovanni G, Di Mascio M, et al. SB 242084, men. Am J Hum Genet 1991;48:677–681. a selective serotonin2C receptor antagonist increases dopami- 51. Harada S, Agarwal DP, Goedde HW. Aldehyde dehydrogenase nergic transmission in the mesolimbic system. Neuropharmacol- deficiency as cause of facial flushing reaction to alcohol in Japa- ogy 1999;38(8):1195–205. nese. Lancet 1982;2(8253):982. 30. King GR, Xiong Z, Ellinwood EH. Blockade of accumbens 5- 52. Chen Y-C, Lu R-B, Peng G-S, et al. Alcohol metabolism and HT3 receptor down-regulation by ondansetron administered cardiovascular response in an alcoholic patient homozygous for during continuous cocaine administration. Eur J Pharmacol the ALDH2-2 variant gene allele. Alcohol Clin Exp Res 1999; 1999;364(2–3):79–87. 23(12):1853–1860. 31. Yoshimoto K, Yayama K, Sorimachi Y, et al. Possibility of 5- 53. Tu GC, Israel Y. Alcohol consumption by orientals in North HT3 receptor involvement in alcohol dependence: a microdia- America is predicted largely by a single gene. Behav Genet 1995; lysis study of nucleus accumbens dopamine and serotonin re- 25(1):59–65. lease in rats with chronic alcohol consumption. Alcohol Clin 54. Goldman D. Genetic transmission. In:Galanter M, ed. Recent Exp Res 1996;20(9 suppl):311A–319A. developments in alcoholism, vol 11: ten years of progress. New 32. Jarvik ME, Schneider NG. Nicotine. In: Lowinson JH, Ruiz York: Plenum Press, 1993;14:231–248. P, Millman RB, eds. Substance abuse: a comprehensive textbook, 55. Neumark YD, Friedlander Y, Thomasson HR, Li TK. Associa- second ed. Baltimore: Williams & Wilkins, 1992:334–356. tion of the ADH2-2 allele with reduced ethanol consumption 33. Markou A, Kosten TR, Koob GF. Neurobiological similarities in Jewish men in Israel: a pilot study. J Stud Alcohol 1998;59(2): in depression and drug dependence: a self medication hypothe- 133–139. sis. Neuropsychopharmacology 1998;18(3):135–174. 56. Monteiro MG, Klein JL, Schuckit MA. High levels of sensitivity 1422 Neuropsychopharmacology: The Fifth Generation of Progress

to alcohol in young adult Jewish men: a pilot study. J Stud related traits with a polymorphism in the serotonin transporter Alcohol 1991;52(5):464–469. gene regulatory region. Science 1996;274(5292):1527–1531. 57. Thomasson HR, Beard JD, Li TK. ADH2 gene polymorphisms 78. Mazzanti CM, Lappalainen J, Long JC, et al. Role of the seroto- are determinants of alcohol pharmacokinetics. Alcohol Clin Exp nin transporter promoter polymorphism in anxiety-related Res 1995;19(6):1494–1499. traits. Arch Gen Psychiatry 1998;55:936–940. 58. McCarver DG, Thomasson HR, Martier SS, et al. Alcohol de- 79. Hammoumi S, Payen A, Favre JD, et al. Does the short variant hydrogenase-2-3 allele protects against alcohol-related birth de- of the serotonin transporter linked polymorphic region consti- fects among African Americans. J Pharmacol Exp Ther 1997; tute a marker for alcohol dependence? Alcohol 1999;17(2): 283(3):1095–1101. 107–112. 59. Lander ES, Schork NJ. Genetic dissection of complex traits. 80. Sander T, Harms H, Lesch KP, et al. Association analysis of a Science 1994;265:2037–2048. regulatory variation of the serotonin transporter gene with severe 60. Risch N, Merikangas K. The future of genetic studies of com- alcohol dependence. Alcohol Clin Exp Res 1997;21(8): plex human diseases. Science 1996;273:1516–1517. 1356–1359. 61. Spielman RS, McGinnis RE, Ewens WJ. Transmission test for 81. Hallikainen T, Saito T, Lachman HM, et al. Association be- linkage disequilibrium: the gene region and insulin-de- tween low activity serotonin transporter promoter genotype and pendent diabetes mellitus (IDDM). Am J Hum Genet 1993;52: early onset alcoholism with habitual impulsive violent behavior. 506–516. Mol Psychiatry 1999;4(4):385–388. 62. Ewens WJ, Spielman RS. The transmission/disequilibrium test: 82. Edenberg HJ, Reynolds J, Koller DL, et al. A family-based history, subdivision, and admixture. Am J Hum Genet 1995; analysis of whether the functional promoter alleles of the seroto- 57:455–464. nin transporter gene HTT affect the risk for alcohol depen- 63. Pritchard JK, Rosenberg NA. Use of unlinked genetic markers dence. Alcohol Clin Exp Res 1998;22(5):1080–1085. to detect population stratification in association studies. Am J 83. Ishiguro H, Saito T, Akazawa S, et al. Association between Hum Genet 1999;65:220–228. drinking-related antisocial behavior and a polymorphism in the 64. Buck KJ, Metten P, Belknap JK, et al. Quantitative trait loci serotonin transporter gene in a Japanese population. Alcohol involved in genetic predisposition to acute alcohol withdrawal Clin Exp Res 1999;23(7):1281–1284. in mice. J Neurosci 1997;17(10):3946–3955. 84. Schuckit MA, Mazzanti C, Smith TL, et al. Selective genotyping 65. Buck KJ, Hood HM. Genetic association of a GABA(A) recep- for the role of 5-HT2A, 5-HT2C, and GABAA6 receptors and tor gamma2 subunit variant with severity of acute physiological the serotonin transporter in the level of response to alcohol: a dependence on alcohol. Mamm Genome 1998;9(12):975–978. pilot study. Biol Psychiatry 1999;45:647–651. 66. Crabbe JC, Belknap JK, Mitchell SR, et al. Quantitative trait 85. Gelernter J, Kranzler H, Cubells JF. Serotonin transporter pro- loci mapping of genes that influence the sensitivity and tolerance tein (SLC6A4) allele and haplotype frequencies and linkage dis- to ethanol-induced hypothermia in BXD recombinant inbred equilibria in African- and European-American and Japanese mice. J Pharmacol Exp Ther 1994;269(1):184–192. populations and in alcohol-dependent subjects. Hum Genet 67. Crabbe JC, Buck KJ, Metten P, et al. Strategies for identifying 1997;101(2):243–246. genes underlying drug abuse susceptibility. In: Lee TNH, ed. 86. Nielsen DA, Goldman D, Virkkunen M, et al. Suicidality and Molecular approaches to drug abuse research, vol 3. NIDA Res 5-hydroxyindole acetic acid concentration associated with a Monogr 1996;161:201–219. polymorphism. Arch Gen Psychiatry 1994;51(1):34–38. 68. Crabbe JC, Phillips TJ, Feller DJ, et al. Elevated alcohol con- 87. Nielsen DA, Virkkunen M, Lappalainen J, et al. A tryptophan sumption in null mutant mice lacking 5-HT1B serotonin recep- hydroxylase gene marker for suicidality and alcoholism. Arch tors. Nat Genet 1996;14(1):98–101. Gen Psychiatry 1998;55:593–602. 69. Rocha BA, Scearce-Levie K, Hen R. Increased vulnerability to 88. Fletcher PJ, Korth KM. Activation of 5-HT1B receptors in the cocaine in mice lacking the serotonin-1B receptor. Nature 1998; nucleus accumbens reduces amphetamine-induced enhance- 393(6681):175–178. ment of responding for conditioned reward. Psychopharmacol 70. Rubinstein M, Phillips TJ, Bunzow JR, et al. Mice lacking dopa- (Berl) 1999;142(2):165–174. mine D4 receptors are supersensitive to ethanol, cocaine and 89. Boulenguez P, Rawlins JN, Chauveau J, et al. Modulation of methamphetamine. Cell 1997;90:991–1001. dopamine release in the nucleus accumbens by 5-HT1B ago- 71. Phillips TJ, Brown KJ, Burkhart-Kasch S, et al. Alcohol prefer- nists: involvement of the hippocampo-accumbens pathway. ence and sensitivity are markedly reduced in mice lacking dopa- Neuropharmacology 1996;35(11):1521–1529. mine D2 receptors. Nat Neurosci 1998;1(7):610–615. 90. Lappalainen J, Long JC, Eggert M, et al. Linkage of antisocial 72. Wang YM, Gainetdinov RR, Fumagalli F, et al. Knockout of alcoholism to the serotonin 5-HT1B receptor gene in 2 popula- the vesicular monoamine transporter 2 gene results in neonatal tions. Arch Gen Psychiatry 1998;55(11):989–994. death and supersensitivity to cocaine and amphetamine. Neuron 91. Willins DL, Meltzer HY. Serotonin 5-HT2C agonists selec- 1997;19(6):1285–1296. tively inhibit morphine-induced dopamine efflux in the nucleus 73. Berrettini WH, Ferraro TN, Alexander RC, et al. Quantitative accumbens. Brain Res 1998;781(1–2):291–299. trait loci mapping of three loci controlling morphine preference 92. Lappalainen J, Long JC, Virkkunen M, et al. HTR2C Cys23Ser using inbred mouse strains. Nat Genet 1994;7:54. polymorphism in relation to CSF monoamine metabolite con- 74. Grisel JE, Metten P, Hughes AM, et al. DBA/2J Mice like beer. centrations and DSM-III-R psychiatric diagnoses. Biol Psychia- RSA abstract 52. Alcohol Clin Exp Res 1998;suppl 22(3):12A. try 1999;46:821–826. 75. Linnoila M, Virkkunen M, Roy A. Biochemical aspects of ag- 93. Lovinger DM. 5-HT3 receptors and the neural actions of alco- gression in man. Clin Neuropharmacol 1986;9(suppl 4): hols: an increasingly exciting topic. Neurochem Int 1999;35: 377–379. 125–130. 76. Heinz A, Ragan P, Jones DW, et al. Reduced central serotonin 94. Iwata N, Cowley DS, Radel M, et al. Relationship between a transporters in alcoholism. Am J Psychiatry 1998;155(11): GABAA␣6 Pro385Ser substitution and benzodiazepine sensitiv- 1544–1549. ity. Am J Psychiatry 1999;156:1447–1449. 77. Lesch KP, Bengel D, Heils A, et al. Association of anxiety- 95. Loh EW, Smith I, Murray R, et al. Association between variants Chapter 99: Molecular and Cellular Genetics of Alcohol Addiction 1423

at the GABAAbeta2, GABAAalpha6 and GABAAgamma2 gene 104. Town T, Abdullah L, Crawford F, et al. Association of a func- -118A) with alcohol depenם) cluster and alcohol dependence in a Scottish population. Mol tional mu-opioid receptor allele Psychiatry 1999;4(6):539–544. dency. Am J Med Genet 1999;88(5):458–461. 96. Sander T, Ball D, Murray R, et al. Association analysis of se- 105. Bergen AW, Kokoszka J, Peterson R, et al. Mu opioid receptor quence variants of GABA(A) alpha 6, beta 2, and gamma2 gene gene variants: lack of association with alcohol dependence. Mol cluster and alcohol dependence. Alcohol Clin Exp Res 1999; Psychiatry 1997;2:490–494. 23(3):427–431. 106. Sander T, Gscheidel N, Wendel B, et al. Human mu-opioid 97. Parsian A, Cloninger CR. Human GABAA receptor alpha 1 receptor variation and alcohol dependence. Alcohol Clin Exp Res and alpha 3 subunits genes and alcoholism. Alcohol Clin Exp 1998;22(9):2108–2110. Res 1997;21(3):430–433. 107. Gelernter J, Kranzler H, Cubells JF. Genetics of two mu opioid 98. Paterson AD, Sunohara GA, Kennedy JL. Dopamine D4 recep- receptor gene (OPRM1) exon 1 polymorphisms: population tor gene: novelty or nonsense? Neuropsychopharmacology 1999; studies, and allele frequencies in alcohol- and drug-dependent 21(1):3–16. subjects. Mol Psychiatry 1999;4(5):476–483. 99. Goldman D, Urbanek M, Guenther D, et al. Linkage and asso- 108. Boyd RT. The molecular biology of neuronal nicotinic acetyl- ciation of a functional DRD2 variant (Ser311Cys) and DRD2 choline receptors. Crit Rev Toxicol 1997;27:299–318. markers to alcoholism, substance abuse and schizophrenia in 109. Silverman MA, Neale MC, Sullivan PF, et al. Haplotypes of four novel single nucleotide polymorphisms in the nicotinic Southwestern American Indians. Am J Med Genet (Neuropsychi- ␤ atr Genet) 1997;74:386–394. acetylcholine receptor 2-subunit (CHRNB2) gene show no association with smoking initiation or nicotine dependence. Am 100. Goldman D, Urbanek M, Guenther D, et al. A functionally J Med Genet 2000;96:646–653. deficient DRD2 variant (Ser311Cys) is not linked to alcoholism 110. Picciotto MR, Zoli M, Rimondini R, et al. Acetylcholine recep- and substance abuse. Alcohol 1998;16(1):47–52. tors containing the beta2 subunit are involved in the reinforcing 101. Ishiguro H, Arinami T, Saito T, et al. Association study between properties of nicotine. Nature 1998;391(6663):173–177. the -141C Ins/Del and TaqI A polymorphisms of the dopamine 111. Long JC, Knowler WC, Hanson RL, et al. Evidence for genetic D2 receptor gene and alcoholism. Alcohol Clin Exp Res 1998: linkage to alcohol dependence on chromosomes 4 and 11 from 22(4):845–848. an autosome-wide scan in an American Indian population. Am 102. Ueno S, Nakamura M, Mikami M, et al. Identification of a J Med Genet (Neuropsychiatr Genet) 1998;81:216–221. novel polymorphism of the human dopamine transporter 112. Reich T, Edenberg HJ, Goate A, et al. Genome-wide search (DAT1) gene and the significant association with alcoholism. for genes affecting the risk for alcohol dependence. Am J Med Mol Psychiatry 1999;4(6):552–557. Genet 1998;81(3):207–215. 103. Gianoulakis C. Implications of endogenous opioids and dopa- 113. Begleiter H, Porjesz B, Reich T, et al. Quantitative trait loci mine in alcoholism: human and basic science studies. Alcohol analysis of human event-related brain potentials: P3 voltage. Alcohol Suppl 1996;1:33–42. Electroencephalogr Clin Neurophysiol 1998;108:244–250.

Neuropsychopharmacology: The Fifth Generation of Progress. Edited by Kenneth L. Davis, Dennis Charney, Joseph T. Coyle, and Charles Nemeroff. American College of Neuropsychopharmacology ᭧ 2002.